Promises Made During Scottish Campaign Will Affect Rest of U.K.—and Europe

For much of Britain, the events of the past few weeks came as a profound shock. Most Britons had taken it for granted that the U.K. was an island of stability in a troubled continent. Many spent the past five years predicting the imminent collapse of the eurozone. Few imagined that the union between England and Scotland might collapse first.

Scotland's vote to remain in the U.K. by a margin of 55% to 45% may have removed that risk—at least for now. But the shock waves will continue to reverberate not only across the U.K....